1. Field of the Invention
The present invention relates to a method of preparing .alpha.-substituted cyanoacetic acid alkyl esters by the reaction of an .alpha.,.beta.-olefin-unsaturated nitrile with an alkanol and carbon monoxide in the presence of Co.sub.2 (CO).sub.8 and a basically acting organic compound at elevated temperatures and pressures.
2. Discussion of the Prior Art
In a method described by Cope et al in "Org. Reactions" 9 (1957), 262-271 for the preparation of .alpha.-alkyl-substituted cyanoacetic acid esters, cyanoacetic acid ester is reacted with an alkyl halide in the presence of an alkali alcoholate and alcohol. This known method requires several expensive reaction steps and produces a considerable amount of by-products and wastes, such as inorganic salts, in addition to the desired products. This method thus becomes very uneconomical. In addition, the inorganic wastes, especially in processes performed on a commercial scale, are ballast materials which are difficult to dispose of in an ecologically sound manner.
Another known method of preparing 2-cyanopropionic acid esters (Belgian Pat. No. 828,187) consists in the reaction of cyanoacetic acid esters with formaldehyde and hydrogen in the presence of glacial acetic acid, palladium on charcoal and, for example, piperidine and hydroquinone. The yields obtained, however, are poor, ranging between 14 and 61 percent.
It is furthermore known from Japanese Examined Patent Appln. 31651/70 to react acrylonitrile with ethanol or propanol or isopropanol and carbon monoxide in the presence of Co.sub.2 (CO).sub.8. In addition to other reaction products, 2-cyanopropionic acid ethyl, n-propyl and isopropyl esters are produced, respectively, in a yield not exceeding 13 percent. The methyl ester cannot be prepared by this method.
Furthermore, a method is known from Japanese Examined Patent Appln. 17246/67 in which acrylonitrile is reacted with carbon monoxide and methanol in the presence of Co.sub.2 (CO).sub.8, pyridine and up to 10 weight percent of H.sub.2, with respect to carbon monoxide, to form mixtures of 2- and 3-cyanoacetic acid methyl ester, .beta.-cyanopropionaldehydedimethylacetal and propionitrile. The same findings are reported also in Bull. Chem. Soc., Japan, 40, 135-144 (1967).
This last-mentioned carbonylation method yields, in addition to 2-cyanopropionic acid methyl ester, considerable amounts of by-products whose separation is made difficult by close boiling points. Another disadvantage lies in the necessity of adding up to 10 weight percent of hydrogen to the carbon monoxide.
It is an object of this invention, therefore, to provide a readily available method for the preparation of .alpha.-substituted cyanoacetic acid alkyl esters whereby such .alpha.-substituted cyanoacetic acid alkyl esters can be prepared in a simple manner in a high yield from readily available materials which do not require expensive reaction steps or provide large quantities of materials which cannot be disposed of readily in an ecological manner.